U.S. patent number 6,764,804 [Application Number 10/316,792] was granted by the patent office on 2004-07-20 for adhesive imaging member with composite carrier sheet.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to William Baum, Robert P. Bourdelais, Timothy J. Giarrusso, Cheryl J. Kaminsky, John M. Palmeri, Philip J. Smith.
United States Patent |
6,764,804 |
Bourdelais , et al. |
July 20, 2004 |
Adhesive imaging member with composite carrier sheet
Abstract
The invention relates to an imaging element comprising a
pragmatic imaging sheet comprising paper having a resin coat on
each side, adhesively adhered to a carrier sheet with a
pressure-sensitive adhesive, comprising at least one core layer of
polyester and a rough lower surface layer.
Inventors: |
Bourdelais; Robert P.
(Pittsford, NY), Kaminsky; Cheryl J. (Webster, NY),
Palmeri; John M. (Hamlin, NY), Baum; William (Rochester,
NY), Smith; Philip J. (Webster, NY), Giarrusso; Timothy
J. (Rochester, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
32325923 |
Appl.
No.: |
10/316,792 |
Filed: |
December 11, 2002 |
Current U.S.
Class: |
430/201; 347/106;
430/259; 430/262; 430/263; 430/496; 430/533 |
Current CPC
Class: |
B41M
5/506 (20130101); B41M 5/508 (20130101); G03C
1/79 (20130101); G03C 1/805 (20130101); B41M
5/502 (20130101) |
Current International
Class: |
B41M
5/50 (20060101); B41M 5/52 (20060101); G03C
1/805 (20060101); G03C 1/79 (20060101); G03C
1/775 (20060101); B41M 5/00 (20060101); G03C
001/765 (); G03C 001/795 (); G03C 001/805 (); B41J
003/407 () |
Field of
Search: |
;430/201,259,262,263,496,533 ;347/106 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Leipold; Paul A.
Claims
What is claimed is:
1. An imaging element comprising an imaging layer, a pragmatic
imaging sheet comprising paper having a resin coat on each side,
adhesively adhered to a carrier sheet with a pressure-sensitive
adhesive, wherein said carrier sheet comprises at least one core
layer of polyester and a rough lower back surface layer wherein
said back surface has a roughness of between 0.18 and 0.6
micrometers.
2. The imaging element of claim 1 wherein said resin coat on each
side of said paper comprises polyethylene.
3. The imaging element of claim 1 wherein said resin coat on each
side of said paper comprises polypropylene.
4. The imaging element of claim 1 wherein said rough back surface
layer comprises polyethylene.
5. The imaging element of claim 1 wherein said carrier sheet has a
stiffness of between 15 and 30 millinewtons in any direction.
6. The imaging element of claim 1 wherein said carrier sheet has a
thickness of between 50 micrometers and 100 micrometers.
7. The imaging element of claim 1 wherein the upper surface of said
carrier sheet comprises a substantially crosslinked silicone
layer.
8. The imaging element of claim 1 wherein the upper surface of said
carrier sheet comprises a non-photoactive substantially crosslinked
silicone layer.
9. The imaging element of claim 8 wherein said silicone layer has a
density stability of 0.03.
10. The imaging element of claim 1 wherein said adhesive has a peel
strength of greater than 150 grams per 5 centimeters.
11. The imaging element of claim 1 wherein said adhesive has a peel
strength of between 15 and 100 grams per 5 centimeters.
12. The imaging element of claim 1 wherein the peel strength
between said pragmatic sheet and said carrier sheet is between 30
and 50 grams per 5 centimeters.
13. The imaging element of claim 1, wherein the peel strength
between said pragmatic sheet and said carrier sheet is between 35
and 45 grams per 5 centimeters.
14. The imaging element of claim 1 wherein said carrier sheet has a
curl of less than 15 curl units over a temperature range of between
0 to 100.degree. C.
15. The imaging element of claim 1 wherein said adhesive has a
resistivity of less than 10.sup.12.
16. The imaging element of claim 1 wherein said adhesive comprises
an antioxidant.
17. The imaging element of claim 1 wherein said pragmatic imaging
sheet comprises at least one ink jet receiving layer.
18. The imaging element of claim 1 wherein said pragmatic imaging
sheet comprises at least one photosensitive silver halide image
forming layer.
19. The imaging element of claim 1 wherein said pragmatic imaging
sheet comprises at least one thermal dye receiving layer.
20. The imaging element of claim 1 wherein said carrier sheet
comprises at least one layer of voided polyester.
21. The imaging element of claim 1 wherein said adhesive comprises
pigment.
22. The imaging element of claim 1 wherein said carrier sheet
comprises at least one layer comprising a colored pigment.
23. The imaging element of claim 1 wherein said pragmatic imaging
sheet has a modulus of greater than 2000 MPa.
24. The imaging element of claim 1 wherein said pragmatic imaging
sheet has a modulus between 2000 and 4000 MPa.
25. The imaging element of claim 1 wherein said pragmatic imaging
sheet has a thickness of between 400 and 500 micrometers.
26. The imaging element of claim 1 wherein said carrier sheet has a
polyethylene layer of both sides.
Description
FIELD OF THE INVENTION
The invention relates to adhesive imaging materials. In a preferred
form it relates to the use of silver halide pressure sensitive
reflective media for the printing images that can be post processed
laminated to display substrates.
BACKGROUND OF THE INVENTION
Prior art photographic albums typically require the consumer to
manually insert conventional prints into a classic sleeve, or use
adhesive to bond conventional prints to blank album pages. This is
a time consuming, difficult operation that provides less than
satisfactory results. Consumers often procrastinate and do not
place prints in albums when they receive them from the
photofinisher, risking loosing time and event references. When
adhesives are used to maintain the prints in the album, alignment
becomes critical. Additionally, many adhesives can damage a print
and often fail after time, thus, allowing the prints to fall out of
the album. Also, in addition to purchasing separate binder album
pages, adhesive and other items may need to be purchased.
Professional photographic labs currently provide high quality
images to the advertising and display industry for product
advertising, point of purchase displays and trade show graphics.
Presently, the lab print images using silver halide or ink jet
imaging technology onto standard high quality paper and post
printing laminate the images to substrates that provide structure
to the image for display. The lamination of the image to the
substrate typically occurs with a double sided pressure sensitive
tape. It would be desirable if the use of the lamination tape could
be eliminated to improve the efficiency of the work flow in the
professional labs.
It is well known in the pressure sensitive adhesive industry to
provide a pressure sensitive adhesive removability feature by
carefully controlling the pressure sensitive adhesive coat weight
within a certain range. While controlling the coat weight of the
pressure sensitive adhesive does provide removability of the
pressure sensitive adhesive for a period of time, the activation
time for pressure adhesive with controlled coat weight varies
considerably because of coat weight variation in the manufacturing
operation. Repositioning pressure sensitive adhesive with
controlled coat weight applied to image media would result in
unpredictable repositioning time and ultimate bond strength for
consumers and therefore would not be suitable for scrapbook and
album applications were a predictable repositioning time and
ultimate strength are required.
In U.S. Pat. No. 6,045,965, a photographic member with a peelable
and repositioning adhesive member is discussed. While the adhesive
discussed in U.S. Pat. No. 6,045,965 does reposition to a variety
of surfaces, the adhesive formulations disclosed do not form
permanent bonds between the photographic member and cellulose paper
album pages. Therefore, the photographic member is not optimized
for scrapbooks and albums were a permanent bond is valued. Further,
the imaging member described in U.S. Pat. No. 6,045,965 disclose a
thin, durable polymer sheet for repositioning an image. While the
thin durable sheet does have high value for most consumer
applications, lamination of the print to surfaces that are rough
typically requires a base that is thick and strong to reduce the
amount of image side embossing by rough lamination surfaces such as
painted walls, cellulose paper board, fabric and flooring
surfaces.
Typically pressure sensitive labels are supplied with a liner web
material that allows the pressure sensitive label to be transported
though the printing process and converting process while protecting
the adhesive. Prior art liner materials typically comprise a coated
paper or a thin polymer liner onto which a release coating is
subsequently provided. Liner materials typically utilized in the
pressure sensitive label are not suitable for a photographic
images. Problems such as photographic reactivity with the light
sensitive layers, lack of stiffness of the liner, and edge
penetration of processing chemistry into the paper used as a liner
prevent typical polymer and paper liners from being utilized for
photographic pressure sensitive labels.
PROBLEM TO BE SOLVED BY THE INVENTION
There is a need for pressure sensitive imaging media that utilizes
a liner material that can be efficiently conveyed through the image
creation process while maintaining the quality of the image.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
improved photograph and album system.
It is another object of the present invention to provide a base
material that reduces the amount of image side embossing in
lamination applications.
It is still yet another object of the present invention to provide
a liner material that allows for efficient transport through
printing and processing of images.
These and other objects of the invention are accomplished by an
imaging element comprising an imaging layer, a pragmatic imaging
sheet comprising paper having a resin coat on each side, adhesively
adhered to a carrier sheet with a pressure-sensitive adhesive,
wherein said carrier sheet comprises at least one core layer of
polyester and a rough lower surface layer.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention provides improved image quality for imaging adhesive
media materials. The invention also significantly reduces the
amount of image side embossing caused by pressure sensitive
lamination to rough surfaces.
DETAILED DESCRIPTION OF THE INVENTION
The invention has numerous advantages over prior practices in the
art. The invention provides a photographic element that may be
subjected to conventional photographic exposure and development
processes and then peeled to form photographic elements that may be
adhered to surfaces. These photographic elements may be in flexible
sticker form. In another embodiment, the invention provides a
method of incorporating means for dry mounting photographs to
photograph albums. Further the photographs of the invention after
peeling may be mounted to many non-traditional surfaces such as
books, posters, school lockers, office walls, file cabinets and
refrigerators. The materials if adhered to illuminated substrates
such as lamp shades or windows may provide a illuminated image.
Photographs of the invention may also be adhered back to back to
form pages in a book, album or a technical report.
The invention reduces the amount of front side embossing as the
imaging element is laminated to rough surfaces such as walls or
rigid foam boards, when compared to polymer film base materials.
The thickness and modulus of the imaging sheets provides sufficient
thickness and compliance as to significantly reduce front side
embossing of the imaging layers from rough surfaces. The invention
further provides a tough carrier sheet that is removed prior to
lamination of the imaging element. The tough carrier sheet is
provided with the required roughness profile to allow for efficient
transport though printing machines such as ink jet printers,
thermal dye transfer printers and photographic printers. Further,
the tough carrier sheet remains dimensionally stable during
pressure sensitive lamination of the pragmatic sheet to the carrier
sheet in manufacturing. Prior art carrier sheets that are thin
typically suffer from shrinkage in the drying section of the
pressure sensitive lamination machines.
Because the invention materials are thick, they can easily be
handled by persons constructing photographic albums compared to
prior art adhesive prints which comprise thin durable polymer film
base imaging sheets. The thick pragmatic paper sheet also
significantly reduces the amount of front side embossing the occurs
when imaging elements are laminated to rough surfaces such as walls
or cardboard. These and other advantages will be apparent from the
detailed description below.
The terms as used herein, "top", "upper", "emulsion side", and
"face" mean the side or toward the side of a photographic member
bearing the imaging layers. The terms "bottom", "lower side", and
"back" mean the side or toward the side of the photographic member
opposite from the side bearing the photosensitive imaging layers or
developed image. The term used herein "peelable adhesive" or
"repositionable adhesive" means an adhesive material that has a
peel strength less than 100 grams/cm. The term used herein
"permanent adhesive" means as adhesive materials that has a peel
strength of greater than 100 grams/cm. The term used herein
"substrate" means materials that are commonly utilized in the
advertising and display industry for the lamination of images.
Examples include acrylic sheets, paper board, wall board, fabric,
cardboard and polymer sheets.
In order to provide an imaging element that significantly reduces
front side embossing caused by lamination to a rough surface and
provide a web material that is efficiently transported thought
printer equipment an imaging element comprising a pragmatic imaging
sheet comprising paper having a resin coat on each side, adhesively
adhered to a carrier sheet with a pressure-sensitive adhesive,
comprising at least one core layer of polyester and a rough lower
surface layer is preferred. By providing a carrier sheet comprising
at least one layer of polyester, the carrier sheet is both tough
and thin. The lower surface layer comprising a rough layer provides
a rough surface for efficient conveyance through manufacturing,
printing and processing. The polyester core of the preferred
carrier sheet also provides dimensional stability during the
manufacturing step of drying of the pressure sensitive adhesive.
The pragmatic sheet of the invention comprising paper and polymer
layers provides a thick sheet minimizing front side embossing
caused by lamination to surfaces that are rough. Further, the paper
utilized in the pragmatic sheet provides antistatic properties as
it contains both salt and moisture.
The pragmatic imaging sheet suitably has a thickness of greater
than 100 micrometers. The preferred thickness is between 400 and
500 micrometers to best provide the ability to be placed over a
rough surface without showing the roughness in the print. The
modulus of the pragmatic imaging sheet is suitably greater than
2000 MPa. The preferred modulus is between 2000 and 4000 MPa for
good handling properties and the ability to conceal mounting
surface roughness.
The resin coating on each side of the paper preferably comprises
polyethylene. Polyethylene is low in cost, is easily extrudable
thought extrusion slot dies and can contain inorganic chemistry
useful in the formation of images. Examples of useful chemistry
includes the use of white pigments such as TiO.sub.2, barium
sulfate, ZnO, calcium carbonate or optical brighteners. In another
preferred embodiment of the invention, the resin coat on each side
of the paper comprises polypropylene. Polypropylene is low in cost,
can be processed thought a slit die and has a higher mechanical
modulus than polyethylene resulting in a image element that is
tougher and more tear resistant that polyethylene.
The rough back surface layer of the carrier sheet preferably
comprises polyethylene. Polyethylene has been shown to replicate
the surface of rough chilled roller and has the required
coefficient of friction for transport in many silver halide
printers, ink jet printers and thermal dye transfer printers.
Further, polyethylene is soft and does not typically emboss
subsequent image layers when the imaging element is wound into a
roll for efficient printing.
The coefficient of friction or COF of the carrier sheet is an
important characteristic as the COF is related to conveyance and
forming efficiency in printing equipment. COF is the ratio of the
weight of an item moving on a surface to the force that maintains
contact between the surface and the item. The mathematical
expression for COF is as follows:
The COF of the carrier sheet is measured using ASTM D-1894
utilizing a stainless steel sled to measure both the static and
dynamic COF of the carrier. The preferred COF for the liner of the
invention is between 0.2 and 0.6. The coefficient of static
friction is the value at the time movement between the two surfaces
is ready to start but no actual movement has occurred. The
coefficient of kinetic friction refers to the case when the two
surfaces are actually sliding against each other at a constant rate
of speed. COF is usually measured by using a sled placed on the
surface. The force necessary at the onset of sliding provides a
measurement of static COF. Pulling the sled at a constant speed
over a given length provides a measure of kinetic frictional
force.
The back surface of the carrier sheet forming the back of the image
element preferably has a roughness of between 0.18 and 0.6
micrometers. This range has been show to provide efficient
transport through imaging printers and processors. Back surface
roughness less than 0.15 micrometers has been shown to slip and
loose registration. Surface roughness greater than 0.70 has been
shown to emboss the imaging layers in a wound roll, especially,
gelatin based silver halide imaging layers.
In a preferred embodiment, the surface roughness of the carrier
sheet is in the form of a plurality of random microlenses, or
lenslets. The microlenses have been shown to provide excellent
conveyance through manufacturing and printing. The microlenses can
also be easily heat embossed to provide branding on the imaging
element without the use of expensive ink as the lenses very
efficiently diffuse visible reflected light and create high
contrast between thermally embossed areas and the lenses. The term
"lenslet" means a small lens, but for the purposes of the present
discussion, the terms lens and lenslet may be taken to be the same.
The lenslets overlap to form complex lenses. "Complex lenses" means
a major lens having on the surface thereof multiple minor lenses.
"Major lenses" mean larger lenslets in which the minor lenses are
formed randomly on top of. "Minor lenses" mean lenses smaller than
the major lenses that are formed on the major lens. The plurality
of lenses of all different sizes and shapes are formed on top of
one another to create a complex lens feature resembling a
cauliflower. The lenslets and complex lenses formed by the lenslets
can be concave into the transparent polymeric film or convex out of
the transparent polymeric film. The term "concave" means curved
like the surface of a sphere with the exterior surface of the
sphere closest to the surface of the film. The term "convex" means
curved like the surface of a sphere with the interior surface of
the sphere closest to the surface of the film.
Preferably, the concave or convex lenses utilized to create the
rough surface have an average frequency in any direction of between
4 and 250 complex lenses/mm. When a film has an average of 285
complex lenses/mm creates the width of the lenses approach the
wavelength of light. The lenses will impart a color to the light
passing through the lenses and change the color temperature of the
display. Less than 4 lenses/mm Creates lenses that are too large
and therefore diffuse the light less efficiently. Concave or convex
lenses with an average frequency in any direction of between 22 and
66 complex lenses/mm are most preferred. The preferred rough
surface has concave or convex lenses at an average width between 3
and 60 micrometers in the x and y direction. When lenses have sizes
below 1 micrometer the lenses impart a color shift in the light
passing through because the lenses dimensions are on the order of
the wavelength of light. When the lenses have an average width in
the x or y direction of more than 68 micrometers, the lenses is too
large to diffuse the light efficiently. More preferred, the concave
or convex lenses at an average width between 15 and 40 micrometers
in the x and y direction
The concave or convex complex lenses comprising minor lenses
wherein the diameter of the smaller lenses is preferably less than
80%, on average, the diameter of the major lens. When the diameter
of the minor lens exceeds 80% of the major lens, the diffusion
efficiency is decreased because the complexity of the lenses is
reduced. The concave or convex complex lenses comprising minor
lenses wherein the width in the x and y direction of the smaller
lenses is preferably between 2 and 20 micrometers. When minor
lenses have sizes below 1 micron the lenses impart a color shift in
the light passing through because the lenses dimensions are on the
order of the wavelength of light. When the minor lenses have sizes
above 25 micrometers, the diffusion efficiency is decreased because
the complexity of the lenses is reduced. Most preferred are the
minor lenses having a width in the x and y direction between 3 and
8 micrometers.
Preferably, the concave or convex complex lenses comprise an olefin
repeating unit. Polyolefins are low in cost and easily formed on
the surface of the carrier sheet. Further, polyolefin polymers are
efficiently melt extrudable and therefore can be used to create an
efficient rough surface on the imaging element.
The carrier sheet of the invention preferably has a stiffness
between 15 and 30 millinewtons. Below 10 millinewtons, stripping of
the carrier at time of lamination of the image to useful substrates
such as paper board or acrylic board is difficult. A stiffness
above 40 millinewtons is not cost justified. Further carrier
materials typically discarded and a carrier stiffness between 15
and 30 millinewtons reduces the environmental impact of the
discarded carrier. The carrier sheet of the invention has a
thickness of between 50 and 100 micrometers. This preferred
thickness range balances the ease of use with the environmental
impact of discarded carrier sheet.
The carrier sheet of the invention preferably contains a release
layer for the release of the pressure sensitive adhesive. Without
the release layer the pressure sensitive adhesive would form a
permanent bond between the carrier sheet and the pragmatic sheet.
The release layer allows for uniform separation of the pressure
sensitive adhesive at the pragmatic sheet carrier sheet interface.
The release layer may be applied to the carrier sheet by any method
known in the art for applying a release layer to substrates.
Preferred examples include silicone coatings, tetrafluoroethylene
fluorocarbon coatings, fluorinated ethylene-propylene coatings, and
calcium stearate. Most preferred is a substantially cross linked
silicone system that minimizes the unwanted interaction with
photosensitive imaging layers. A substantially cross linked
silicone system has greater than 98% crosslinking of the silicone.
A cross linked silicone system that has a silver halide density
stability of less than 0.03 is preferred as a density loss of less
than 0.03 is below what customers can visually perceive. The
density stability is measured by keeping an unexposed sample of
light sensitive silver imaging layer applied to the surface of the
pragmatic sheet containing the carrier sheet. The unexposed sample
is kept at 30 degrees Celsius for 7 days at which time the sample
is exposed with a test pattern containing density from 0.0 to 2.0.
The sample is compared with a check material that is coated on
inert polyester.
In a further embodiment of the invention, the core polyester layer
is voided. The voided polyester sheet is high in opacity, has an
increased mechanical modulus and temperature resistance compared to
polyolefin voided materials and is dimensionally stable in dryers
encountered in manufacturing and printing. According to the present
invention a process useful for the production of a voided polymer
core comprises a blend of particles of a linear polyester with from
10 to 40% by weight of particles of a homopolymer or copolymer of
polyolefin, extruding the blend as a film, quenching and biaxially
orienting the film by stretching it in mutually perpendicular
directions, and heat setting the film. Preferred amount of
polyolefin is between 40 and 50% of the total polymer weight of the
vacuous layer as this gives a low cost and low density layer. The
preferred polyolefin is propylene as it is low in cost and
successfully blends with the polyester for extrusion.
The opacity of the resulting voided polymer core carrier sheet
arises through voiding which occurs between the regions of the
linear polyester and the polyolefin polymer during the stretching
operation. The linear polyester component of the voided polymer
core may consist of any thermoplastic film forming polyester which
may be produced by condensing one or more dicarboxylic acids or a
lower alkyl diester thereof, e.g. terephthalic acid, isophthalic,
phthalic, 2,5-, 2,6- or 2,7-naphthalene dicarboxylic acid, succinic
acid, sebacic acid, adipic acid, azelaic acid, bibenzoic acid, and
hexahydroterephthalic acid, or bis-p-carboxy phenoxy ethane, with
one or more glycols, e.g. ethylene glycol, 1,3-propanediol,
1-4-butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol. It
is to be understood that a copolyester of any of the above
materials may be used. The preferred polyester is polyethylene
terephthalate.
The preferred polyolefin. additive which is blended with the
polyester is a homopolymer or copolymer of propylene. Generally a
homopolymer produces adequate opacity in the vacuous polymer and it
is preferred to use homopolypropylene. An amount 10 to 40% by
weight of polyolefin additive, based on the total weight of the
blend, is used. Amounts less than 10% by weight do not produce an
adequate opacifying effect. Increasing the amount of polyolefin
additive causes the tensile properties, such as tensile yield and
break strength, modulus and elongation to break, to deteriorate and
it has been found that amounts generally exceeding about 40% by
weight can lead to film splitting during production. Satisfactory
opacifying and tensile properties can be obtained with up to 35% by
weight of polyolefin additive.
The polyolefin additive preferably used in the carrier sheet of
this invention is incompatible with the polyester component of the
vacuous polymer base and exists in the form of discrete globules
dispersed throughout the oriented and heat set vacuous polymer
base. The opacity of the vacuous polymer base is produced by
voiding which occurs between the additive globules and the
polyester when the vacuous polymer base is stretched. It has been
discovered that the polymeric additive must be blended with the
linear polyester prior to extrusion through the film forming die by
a process which results in a loosely blended mixture and does not
develop an intimate bond between the polyester and the polyolefin
additive.
Such a blending operation preserves the incompatibility of the
components and leads to voiding when the vacuous polymer base is
stretched. A process of dry blending the polyester and polyolefin
additive has been found to be useful. For instance, blending may be
accomplished by mixing finely divided, e.g. powdered or granufar,
polyester and polymeric additive and, thoroughly mixing them
together, e.g. by tumbling them. The resulting mixture is then fed
to the film forming extruder. Blended polyester and polymeric
additive which has been extruded and, e.g. reduced to a granulated
form, can be successfully re-extruded into a vacuous opaque voided
film (vacuous polymer base). It is thus possible to re-feed scrap
film, e.g. as edge trimmings, through the process. Alternatively,
blending may be effected by combining melt streams of polyester and
the polyolefin additive just prior to extrusion. If the polymeric
additive is added to the polymerization vessel in which the linear
polyester is produced, it has been found that voiding and hence
opacity is not developed during stretching. This is thought to be
on account of some form of chemical or physical bonding which may
arise between the additive and polyester during thermal
processing.
The extrusion, quenching and stretching of the voided polymer core
may be effected by any process which is known in the art for
producing oriented polyester film, e.g. by a flat film process or a
bubble or tubular process. The flat film process is preferred for
making vacuous polymer base according to this invention and
involves extruding the blend through a slit die and rapidly
quenching the extruded web upon a chilled casting drum so that the
polyester component of the film is quenched into the amorphous
state. The film base is then biaxially oriented by stretching in
mutually perpendicular directions at a temperature above the
glass-rubber transition temperature of the polyester. Generally the
film is stretched in one direction first and then in the second
direction although stretching may be effected in both directions
simultaneously if desired. In a typical process the film is
stretched firstly in the direction of extrusion over a set of
rotating rollers or between two pairs of nip rollers and is then
stretched in the direction transverse thereto by means of a tenter
apparatus. The film may be stretched in each direction to 2.5 to
4.5 times its original dimension in the direction of stretching.
After the film has been stretched and a vacuous polymer base
formed, it is heat set by heating to a temperature sufficient to
crystallize the polyester whilst restraining the vacuous polymer
base against retraction in both directions of stretching. The
voiding tends to collapse as the heat setting temperature is
increased and the degree of collapse increases as the temperature
increases. Hence the light transmission increases with an increase
in heat setting temperatures. Whilst heat setting temperatures up
to about 230 C. can be used without destroying the voids,
temperatures below 200 C. generally result in a greater degree of
voiding and higher opacity.
The opacity as determined by the total luminous transmission of a
voided polymer core depends upon the thickness of the voided
polymer core. Thus the stretched and heat set voided polymer core
made according to this invention have a total luminous transmission
not exceeding 25%, preferably not exceeding 20%, for vacuous
polymer base having a thickness of at least 100 micrometers, when
measured by ASTM test method D-1003-61. Voided polymer core of
thickness 50 to 99 micrometers have a total luminous transmission
generally up to 30%. The invention also therefore relates to opaque
biaxially oriented and heat set vacuous polymer bases produced from
a blend of a linear polyester and from 10 to 40% by weight of a
homopolymer or copolymer of ethylene or propylene and having a
total luminous transmission of up to 30%. Such vacuous polymer
bases may be made by the process specified above. The globules of
polymeric additive distributed throughout the film produced
according to this invention are generally 5 to 50 micrometer in
diameter and the voids surrounding the globules 3 to 4 times the
actual diameter of the globules. It has been found that the voiding
tends to collapse when the void size is of the order of the vacuous
polymer base thickness. Such vacuous polymer base therefore tends
to exhibit poor opacity because of the smaller number of void
surfaces at which light scattering can occur. Accordingly it is
therefore preferred that the voided polymer core of this invention
should have a thickness of at least 25 microns. Voided polymer core
thickness of between 100 and 250 micrometers are convenient for
most end uses. Because of the voiding, the voided polymer core with
a density of less than 0.7 gm/cc lighter in weight, and more
resilient than those bases with higher densities. The voided
polymer core may contain any compatible additive, such as pigments.
Thus a light reflecting pigment, such as titanium dioxide, may be
incorporated to improve the appearance and whiteness of the voided
polymer core.
Minimizing the curl of the carrier sheet is critical to the
performance of the imaging element during printing, processing and
lamination as curl can lead to jamming in printers. The carrier
sheet of the invention preferably has a curl of less than 15 units.
Curl is minimized, in a preferred embodiment, by placing a
polyethylene layer on each side of the polyester sheet. The curl
test measures the amount of curl in a parabolically deformed
sample. A 8.5 cm diameter round sample of the composite was stored
at the test humidity for 21 days. The amount of time required
depends on the vapor barrier properties of the laminates applied to
the moisture sensitive paper base, and it should be adjusted as
necessary by determining the time to equilibrate the weight of the
sample in the test humidity. The curl readings are expressed in
ANSI curl units, specifically, 100 divided by the radius of
curvature in inches. The radius of curvature is determined by
mounting the sample perpendicular to the measurement surface,
visually comparing the curled shape, sighting along the axis of
curl, with standard curves in the background. The standard
deviation of the test is 2 curl units. The curl may be positive or
negative, and for photographic products, the usual convention is
that the positive direction is curling towards the photosensitive
or imaging layer.
A pressure sensitive imaging element adhesive is utilized in the
invention to allow the printed or developed silver halide image to
be adhered to the surface of the substrates that are typically
utilized in the advertising and display market. "Peelable
separation" or "peel strength" or "separation force" is a measure
of the amount of force required to separate two surfaces that are
held together by internal forces of the pressure sensitive adhesive
which consist of valence forces or interlocking action, or both.
Peel strength is measured using an Instron gauge and peeling the
sample at 180 degrees with a crosshead speed of 1.0 meters/min. The
sample width is 5 cm and the distance peeled is 10 cm in
length.
A peelable pressure sensitve adhesive is utilized to allow the
consumer to separate the imaging element from a display substrate.
Separation of the pragmatic sheet containing the imaging element
would allow, for example, an image to be repositioned to a wall or
column for a trade show and then moved to a new location. The
preferred peel strength between the pragmatic sheet and a substrate
is no greater than 80 grams/cm. A peel strength greater than 100
grams/cm, consumers would begin to have difficulty separating the
image from a substrate. Further, at peel strengths greater than 110
grams/cm, the force is beginning to approach the internal strength
of paper substrate, causing an unwanted fracture of the paper
substrate before the separation of the image.
In another embodiment of the invention, upon separation of the
pragmatic sheet from the carrier sheet, the peelable pressure
sensitive adhesive of this invention has a preferred repositioning
peel strength between 20 grams/cm and 100 grams/cm. Repositioning
peel strength is the amount of force required to peel the separated
image containing an pressure sensitive adhesive from a stainless
steel block at 23.degree. C., and 50% RH. At repositioning peel
strengths less than 15 grams/cm, the pressure sensitive adhesive
lacks sufficient peel strength to remain adhered to a variety of
surfaces such as refrigerators or photo albums. At peel strengths
greater than 120 grams/cm, the pressure sensitive adhesive of this
invention is too aggressive, not allowing the consumer to later
reposition the image.
In a further embodiment of the invention, the pressure sensitive
adhesive has a peel strength greater than 150 grams per 5
centimeters. Peel strengths greater than 150 grams provide a
permanent bond between the pragmatic sheet containing the imaging
layers and various substrates utilized in the display and
advertising market. Further, for gelatin based photographic imaging
elements, the peel force greater than 150 grams resists the curling
forces caused by the shrinking of the gelatin binder used for
silver halide imaging systems.
The pressure sensitive adhesive of this invention may be a single
layer or two or more layers. Suitable peelable pressure sensitive
adhesives of this invention must not interact with the light
sensitive silver halide imaging system so that image quality is
deteriorated. Further, since photographic elements of this
invention must be photoprocessed, the performance of the pressure
sensitive adhesive of this invention must not be deteriorated by
photographic processing chemicals. Suitable pressure sensitive
adhesive may be inorganic or organic, natural or synthetic, that is
capable of bonding the image to the desired surface by surface
attachment. Examples of inorganic pressure sensitive adhesives are
soluble silicates, ceramic and thermosetting powdered glass.
Organic pressure sensitive adhesives may be natural or synthetic.
Examples of natural organic pressure sensitive adhesives include
bone glue, soybean starch cellulosics, rubber latex, gums, terpene,
mucilages and hydrocarbon resins. Examples of synthetic organic
pressure sensitive adhesives include elastomer solvents,
polysulfide sealants, theromplastic resins such as isobutylene and
polyvinyl acetate, theromsetting resins such as epoxy,
phenoformaldehyde, polyvinyl butyral and cyanoacrylates and
silicone polymers.
For single or multiple layer pressure sensitive adhesive systems,
the preferred pressure sensitive adhesive composition is selected
from the group consisting of natural rubber, syntheic rubber,
acrylics, acrylic copolymers, vinyl polymers, vinyl acetate-,
urethane, acrylate- type materials, copolymer mixtures of vinyl
chloride-vinyl acetate, polyvinylidene, vinyl acetate-acrylic acid
copolymers, styrene butadiene, carboxylated stryrene butadiene
copolymers, ethylene copolymers, polyvinyl alcohol, polyesters and
copolymers, cellulosic and modified cellulosic, starch and modified
starch compounds, epoxies, polyisocyanate, polyimides.
Water based pressure sensitive adhesion provide some advantages for
the manufacturing process of non solvent emissions. Repositionable
peelable pressure sensitive adhesive containing non-pressure
sensitive adhesive solid particles randomly distributed in the
pressure sensitive adhesive layer aids in the ability to stick and
then remove the print to get the desired end result. The most
preferred pressure sensitive peelable pressure sensitive adhesive
is a respositionable pressure sensitive adhesive layer containing
at about 5% to 20% by weight of a permanent pressure sensitive
adhesive such as isooctyl acrylate/acrylic acid copolymer and at
about 95% to 80% by weight of a tacky elastomeric material such as
acrylate microspheres with the pressure sensitive adhesive layer
coverage at about 5 to 20 g/m.sup.2.
The preferred peelable pressure sensitive adhesive materials may be
applied using a variety of methods known in the art to produce
thin, consistent pressure sensitive adhesive coatings. Examples
include gravure coating, rod coating, reverse roll coating, and
hopper coating. The pressure sensitive adhesives may be coated on
the liner or the face stock materials prior to lamination. For
single or multiple layer pressure sensitive adhesive systems, the
preferred permanent pressure sensitive adhesive composition is
selected from the group consisting of epoxy, phenoformaldehyde,
polyvinyl butyral, cyanoacrylates, rubber based pressure sensitive
adhesives, styrene/butadiene based pressure sensitive adhesives,
acrylics and vinyl derivatives.
The pressure sensitive adhesives of the invention preferably
contain a pigment. Pigments are well known to add color or
whiteness. The addition of white pigments such as TiO.sub.2 or ZnO
improve the opacity of the pragmatic sheet containing the imaging
elements when applied to the various display substrates. Foe
example, a wedding scene applied to a dark wall would suffer in
quality if the adhesive was not pigmented white as the wedding
dress on the bride would appear dark and low in quality. Colored
pigments are preferably added to the pressure sensitive adhesive of
the invention to build brand awareness and allow for better
contrast when the imaging elements are laminated to display
substrates.
Antioxidants are preferably added to the adhesive layer to reduce
the amount of oxidation in the adhesive layer which results in a
loss of pressure sensitive adhesive properties such as peel force
and shear resistance. The antioxidant addition is particularly
important as the invention materials are dryed in heated dryers in
several points during manufacturing and printing. The antioxidants
help maintain the desirable strength and adhesion properties of the
adhesive.
Since the light sensitive silver halide layers of a preferred
embodiment of the invention can suffer from unwanted exposure from
static discharge during manufacturing, printing and processing, the
pressure sensitive adhesive preferably has a resistivity of less
than 10.sup.11 ohms/square. A wide variety of
electrically-conductive materials can be incorporated into adhesive
layers to produce a wide range of conductivities. These can be
divided into two broad groups: (i) ionic conductors and (ii)
electronic conductors. In ionic conductors charge is transferred by
the bulk diffusion of charged species through an electrolyte. Here
the resistivity of the antistatic layer is dependent on temperature
and humidity. Antistatic layers containing simple inorganic salts,
alkali metal salts of surfactants, ionic conductive polymers,
polymeric electrolytes containing alkali metal salts, and colloidal
metal oxide sols (stabilized by metal salts), described previously
in patent literature, fall in this category. However, many of the
inorganic salts, polymeric electrolytes, and low molecular weight
surfactants used are water-soluble and are leached out of the
antistatic layers during processing, resulting in a loss of
antistatic function. The conductivity of antistatic layers
employing an electronic conductor depends on electronic mobility
rather than ionic mobility and is independent of humidity.
Antistatic layers which contain conjugated polymers, semiconductive
metal halide salts, semiconductive metal oxide particles, etc. have
been described previously. However, these antistatic layers
typically contain a high volume percentage of electronically
conducting materials which are often expensive and impart
unfavorable physical characteristics, such as color, increased
brittleness, and poor adhesion to the antistatic layer.
In a preferred embodiment of this invention the label has an
antistat material incorporated into the liner or in the adhesive
layer. It is desirable to have an antistat that has an electrical
surface resistivity of at least 10.sup.11 log ohms/square. In the
most preferred embodiment, the antistat material comprises at least
one material selected from the group consisting of tin oxide and
vanadium pentoxide.
In another preferred embodiment of the invention antistatic
material are incorporated into the pressure sensitive adhesive
layers. The antistatic material incorporated into the pressure
sensitive adhesive layer provides static protection to the silver
halide layers and reduces the static on the label which has been
shown to aid labeling of containers in high speed labeling
equipment. As a stand-alone or supplement to the carrier comprising
an antistatic layer, the pressure sensitive adhesive may also
further comprise an antistatic agent selected from the group
consisting of conductive metal oxides, carbon particles, and
synthetic smectite clay, or multilayered with an inherently
conductive polymer. In one of the preferred embodiments, the
antistat material is metal oxides. Metal oxides are preferred
because they are readily dispersed in the thermoplastic adhesive
:and can be applied to the polymer sheet by any means known in the
art. Conductive metal oxides that may be useful in this invention
are selected from the group consisting of conductive particles
including doped-metal oxides, metal oxides containing oxygen
deficiencies, metal antimonates, conductive nitrides, carbides, or
borides, for example, TiO.sub.2, SnO.sub.2, Al..sub.2 O.sub.3,
ZrO.sub.3, In.sub.2 O.sub.3, MgO, ZnSb.sub.2 O.sub.6, InSbO.sub.4,
TiB.sub.2, ZrB.sub.2, NbB.sub.2, TaB.sub.2, CrB.sub.2, MoB, WB,
LaB.sub.6, ZrN, TiN, TiC, and WC. The most preferred materials are
tin oxide and vanadium pentoxide because they provide excellent
conductivity and are transparent.
Used herein, the phrase `imaging element` comprises an imaging
support comprising the pragmatic sheet, pressure sensitive adhesive
and the carrier sheet as described above, along with an imaging
layer as applicable to multiple techniques governing the transfer
of an image onto the imaging element. Such techniques include
thermal dye transfer, electrophotographic printing, or ink jet
printing, as well as a support for photographic silver halide
images. As used herein, the phrase "photographic element" is a
material that utilizes photosensitive silver halide in the
formation of images.
The thermal dye image-receiving layer of the imaging elements for
thermal dye transfer of the invention may comprise polymers or
mixtures of polymers that provide sufficient dye density, printing
efficiency and high quality images. For example, polycarbonate,
polyurethane, polyester, polyvinyl chloride,
poly(styrene-co-acrylonitrile), poly(caprolactone), polylatic acid,
saturated polyester resins, polyacrylate resins, poly(vinyl
chloride-co-vinylidene chloride), chlorinated polypropylene,
poly(vinyl chloride-co-vinyl acetate), poly(vinyl chloride-co-vinyl
acetate-co-maleic anhydride), ethyl cellulose, nitrocellulose,
poly(acrylic acid)esters, linseed oil-modified alkyd resins,
rosin-modified alkyd resins, phenol-modified alkyd resins, phenolic
resins, maleic acid resins, vinyl polymers, such as polystyrene and
polyvinyltoluene or copolymer of vinyl polymers with methacrylates
or acrylates, poly(tetrafluoroethylene-hexafluoropropylene),
low-molecular weight polyethylene, phenol-modified pentaerythritol
esters, poly(styrene-co-indene-co-acrylonitrile),
poly(styrene-co-indene), poly(styrene-co-acrylonitrile),
poly(styrene-co-butadiene), poly(stearyl methacrylate) blended with
poly(methyl methacrylate). Among them, a mixture of a polyester
resin and a vinyl chloridevinyl acetate copolymer is preferred,
with the mixing ratio of the polyester resin and the vinyl
chloride-vinyl acetate copolymer being preferably 50 to 200 parts
by weight per 100 parts by weight of the polyester resin. By use of
a mixture of a polyester resin and a vinyl chloride-vinyl acetate
copolymer, light resistance of the image formed by transfer on the
image-receiving layer can be improved.
The dye image-receiving layer may be present in any amount that is
effective for the intended purpose. In general, good results have
been obtained at a concentration of from about 1 to about 10
g/m.sup.2. An overcoat layer may be further coated over the
dye-receiving layer, such as described in U.S. Pat. No. 4,775,657
of Harrison et al.
In another embodiment of the invention, the thermal dye receiving
layer comprises a polyester. Polyesters are low in cost and have
good strength and surface properties. Polyesters have high optical
transmission values that allow for high light transmission and
diffusion. This high light transmission and diffusion allows for
greater differences in the bright and dark projected areas
increasing contrast. In a preferred embodiment of the invention,
the polyesters have a number molecular weight of from about 5,000
to about 250,000 more preferably from 10,000 to 100,000.
The polymers used in the dye-receiving elements of one embodiment
of the invention are condensation type polyesters based upon
recurring units derived from alicyclic dibasic acids (Q) and diols
(L) wherein (Q) represents one or more alicyclic ring containing
dicarboxylic acid units with each carboxyl group within two carbon
atoms of (preferably immediately adjacent) the alicyclic ring and
(L) represents one or more diol units each containing at least one
aromatic ring not immediately adjacent to (preferably from 1 to
about 4 carbon atoms away from) each hydroxyl group or an alicyclic
ring which may be adjacent to the hydroxyl groups. For the purposes
of this invention, the terms "dibasic acid derived units" and
"dicarboxylic acid derived units" are intended to define units
derived not only from carboxylic acids themselves, but also from
equivalents thereof such as acid chlorides, acid anhydrides and
esters, as in each case the same recurring units are obtained in
the resulting polymer. Each alicyclic ring of the corresponding
dibasic acids may also be optionally substituted, e.g. with one or
more C1 to C4 alkyl groups. Each of the diols may also optionally
be substituted on the aromatic or alicyclic ring, e.g. by C1 to C6
alkyl, alkoxy, or halogen.
In another embodiment of the invention, the thermal dye receiving
layer comprises a polycarbonate. The diffusion elements formed out
of polycarbonate are easily melted to form areas of specular and
diffuse transmission. Polycarbonates have high optical transmission
values that allow for high light transmission and diffusion. This
high light transmission and diffusion allows for greater
differences in the bright and dark projected areas increasing
contrast.
Polycarbonates (the term "polycarbonate" as used herein means a
carbonic acid and a diol or diphenol) and polyesters have been
suggested for use in image-receiving layers. Polycarbonates (such
as those disclosed in U.S. Pat. Nos. 4,740,497 and 4,927,803) have
been found to possess good dye uptake properties and desirable low
fade properties when used for thermal dye transfer. As set forth in
U.S. Pat. No. 4,695,286, bisphenol-A polycarbonates of number
average molecular weights of at least about 25,000 have been found
to be especially desirable in that they also minimize surface
deformation that may occur during thermal printing.
Polyesters, on the other hand, can be readily synthesized and
processed by melt condensation using no solvents and relatively
innocuous chemical starting materials. Polyesters formed from
aromatic diesters (such as disclosed in U.S. Pat. No. 4,897,377)
generally have good dye up-take properties when used for thermal
dye transfer. Polyesters formed from alicyclic diesters disclosed
in U.S. Pat. No. 5,387,571 (Daly et al.) and polyester and
polycarbonate blends disclosed in U.S. Pat. No. 5,302,574 (Lawrence
et al.), the disclosure of which is incorporated by reference.
Polymers may be blended for use in the dye-receiving layer in order
to obtain the advantages of the individual polymers and optimize
the combined effects. For example, relatively inexpensive
unmodified bisphenol-A polycarbonates of the type described in U.S.
Pat. No. 4,695,286 may be blended with the modified polycarbonates
of the type described in U.S. Pat. No. 4,927,803 in order to obtain
a receiving layer of intermediate cost having both improved
resistance to surface deformation which may occur during thermal
printing and to light fading which may occur after printing. A
problem with such polymer blends, however, results if the polymers
are not completely miscible with each other, as such blends may
exhibit a certain amount of haze. While haze is generally
undesirable, it is especially detrimental for transparent labels.
Blends that are not completely compatible may also result in
variable dye uptake, poorer image stability, and variable sticking
to dye donors.
In a preferred embodiment of the invention, the alicyclic rings of
the dicarboxylic acid derived units and diol derived units contain
from 4 to 10 ring carbon atoms. In a particularly preferred
embodiment, the alicyclic rings contain 6 ring carbon atoms.
A dye-receiving element for thermal dye transfer comprising a
miscible blend of an unmodified bisphenol-A polycarbonate having a
number molecular weight of at least about 25,000 and a polyester
comprising recurring dibasic acid derived units and diol derived
units, at least 50 mole % of the dibasic acid derived units
comprising dicarboxylic acid derived units containing an alicyclic
ring within two carbon atoms of each carboxyl group of the
corresponding dicarboxylic acid, and at least 30 mole % of the diol
derived units containing an aromatic ring not immediately adjacent
to each hydroxyl group of the corresponding diol or an alicyclic
ring are preferred. This polymer blend has excellent dye uptake and
image dye stability, and which is essentially free from haze. It
provides a receiver having improved fingerprint resistance and
retransfer resistance, and can be effectively printed in a thermal
printer with significantly reduced thermal head pressures and
printing line times. Surprisingly, these alicyclic polyesters were
found to be compatible with high molecular weight
polycarbonates.
Examples of unmodified bisphenol-A polycarbonates having a number
molecular weight of at least about 25,000 include those disclosed
in U.S. Pat. No. 4,695,286. Specific examples include Makrolon 5700
(Bayer AG) and LEXAN 141 (General Electric Co.) polycarbonates.
In a further preferred embodiment of the invention, the unmodified
bisphenol-A polycarbonate and the polyester polymers are blended at
a weight ratio to produce the desired Tg of the final blend and to
minimize cost. Conveniently, the polycarbonate and polyester
polymers may be blended at a weight ratio of from about 75:25 to
25:75, more preferably from about 60:40 to about 40:60.
Among the necessary features of the polyesters for the blends of
the invention is that they do not contain an aromatic diester such
as terephthalate, and that they be compatible with the
polycarbonate at the composition mixtures of interest. The
polyester preferably has a Tg of from about 40 C. to about 100 C.,
and the polycarbonate a Tg of from about 100 C. to about 200 C. The
polyester preferably has a lower Tg than the polycarbonate, and
acts as a polymeric plasticizer for the polycarbonate. The Tg of
the final polyester/polycarbonate blend is preferably between 40 C.
and 100 C. Higher Tg polyester and polycarbonate polymers may be
useful with added plasticizer. Preferably, lubricants and/or
surfactants are added to the dye receiving layer for easier
processing and printing. The lubricants can help in polymer
extrusion, casting roll release, and printability. Preferably, the
polyester dye receiving layer is melt extruded on the outer most
surface of the pragmatic sheet.
Dye-donor elements that are used with the dye-receiving element of
the invention conventionally comprise a support having thereon a
dye containing layer. Any dye can be used in the dye-donor employed
in the invention, provided it is transferable to the dye-receiving
layer by the action of heat. Especially good results have been
obtained with sublimable dyes. Dye donors applicable for use in the
present invention are described, e.g., in U.S. Pat. Nos. 4,916,112;
4,927,803; and 5,023,228. As noted above, dye-donor elements are
used to form a dye transfer image. Such a process comprises
image-wise-heating a dye-donor element and transferring a dye image
to a dye-receiving element as described above to form the dye
transfer image. In a preferred embodiment of the thermal dye
transfer method of printing, a dye donor element is employed which
compromises a poly(ethylene terephthalate) support coated with
sequential repeating areas of cyan, magenta, and yellow dye, and
the dye transfer steps are sequentially performed for each color to
obtain a three-color dye transfer image. When the process is only
performed for a single color, then a monochrome dye transfer image
is obtained.
Thermal printing heads, which can be used to transfer dye from
dye-donor elements to receiving elements of the invention, are
available commercially. There can be employed, for example, a
Fujitsu Thermal Head (FTP-040 MCS001), a TDK Thermal Head F415
HH7-1089, or a Rohm Thermal Head KE 2008-F3. Alternatively, other
known sources of energy for thermal dye transfer may be used, such
as lasers as described in, for example, GB No. 2,083,726A.
A thermal dye transfer assemblage comprises (a) a dye-donor
element, and (b) a dye-receiving element as described above, the
dye-receiving element being in a superposed relationship with the
dye-donor element so that the dye layer of the donor element is in
contact with the dye image-receiving layer of the receiving
element.
When a three-color image is to be obtained, the above assemblage is
formed on three occasions during the time when heat is applied by
the thermal printing head. After the first dye is transferred, the
elements are peeled apart. A second dye-donor element (or another
area of the donor element with a different dye area) is then
brought in register with the dye-receiving element and the process
repeated. The third color is obtained in the same manner.
The electrographic and electrophotographic processes and their
individual steps have been well described in the prior art. The
processes incorporate the basic steps of creating an electrostatic
image, developing that image with charged, colored particles
(toner), optionally transferring the resulting developed image to a
secondary substrate, and fixing the image to the substrate. There
are numerous variations in these processes and basic steps; the use
of liquid toners in place of dry toners is simply one of those
variations.
The first basic step, creation of an electrostatic image, can be
accomplished by a variety of methods. The electrophotographic
process of copiers uses imagewise-photodischarge, through analog or
digital exposure, of a uniformly charged photoconductor. The
photoconductor may be a single-use system, or it may be
rechargeable and reimageable, like those based on selenium or
organic photoreceptors.
In one form, the electrophotographic process of copiers uses
imagewise photodischarge, through analog or digital exposure, of a
uniformly charged photoconductor. The photoconductor may be a
single-use system, or it may be rechargeable and reimageable, like
those based on selenium or organic photoreceptors.
In an alternate electrographic process, electrostatic images are
created ionographically. The latent image is created on dielectric
(charge-holding) medium, either paper or film. Voltage is applied
to selected metal styli or writing nibs from an array of styli
spaced across the width of the medium, causing a dielectric
breakdown of the air between the selected styli and the medium.
Ions are created, which form the latent image on the medium.
Electrostatic images, however generated, are developed with
oppositely charged toner particles. For development with liquid
toners, the liquid developer is brought into direct contact with
the electrostatic image. Usually a flowing liquid is employed, to
ensure that sufficient toner particles are available for
development. The field created by the electrostatic image causes
the charged particles, suspended in a nonconductive liquid, to move
by electrophoresis. The charge of the latent electrostatic image is
thus neutralized by the oppositely charged particles. The theory
and physics of electrophoretic development with liquid toners are
well described in many books and publications.
If a reimageable photoreceptor or an electrographic master is used,
the toned image is transferred to paper (or other substrate). The
paper is charged electrostatically, with the polarity chosen to
cause the toner particles to transfer to the paper. Finally, the
toned image is fixed to the paper. For self-fixing toners, residual
liquid is removed from the paper by air-drying or heating. Upon
evaporation of the solvent, these toners form a film bonded to the
paper. For heat-fusible toners, thermoplastic polymers are used as
part of the particle. Heating both removes residual liquid and
fixes the toner to paper.
When used as ink jet imaging media, the imaging elements or media
typically comprise a coated paper having on at least one surface
thereof an ink-receiving or image-forming layer. If desired, in
order to improve the adhesion of the ink receiving layer to the
support, the surface of the support may be corona-discharge-treated
prior to applying the solvent-absorbing layer to the support or,
alternatively, an undercoating, such as a layer formed from a
halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl
acetate copolymer, can be applied to the surface of the support.
The ink receiving layer is preferably coated onto the support layer
from water or water-alcohol solutions at a dry thickness ranging
from 3 to 75 micrometers, preferably 8 to 50 micrometers.
Any known ink jet receiver layer can be used in combination with
the external polyester-based carrier layer of the present
invention. For example, the ink receiving layer may consist
primarily of inorganic oxide particles such as silicas, modified
silicas, clays, aluminas, fusible beads such as beads comprised of
thermoplastic or thermosetting polymers, non-fusible organic beads
or hydrophilic polymers such as naturally-occurring hydrophilic
colloids and gums such as gelatin, albumin, guar, xantham, acacia,
chitosan, starches and their derivatives, and the like; derivatives
of natural polymers such as functionalized proteins, functionalized
gums and starches, and cellulose ethers and their derivatives, and
synthetic polymers such as polyvinyloxazoline,
polyvinylmethyloxazoline, polyoxides, polyethers, poly(ethylene
imine), poly(acrylic acid), poly(methacrylic acid), n-vinyl amides
including polyacrylamide and polyvinylpyrrolidone, and poly(vinyl
alcohol), its derivatives and copolymers; and combinations of these
materials. Hydrophilic polymers, inorganic oxide particles, and
organic beads may be present in one or more layers on the substrate
and in various combinations within a layer.
A porous structure may be introduced into ink receiving layers
comprised of hydrophilic polymers by the addition of ceramic or
hard polymeric particulates, by foaming or blowing during coating,
or by inducing phase separation in the layer through introduction
of non-solvent. In general, it is preferred for the base layer to
be hydrophilic, but not porous. This is especially true for
photographic quality prints, in which porosity may cause a loss in
gloss. In particular, the ink receiving layer may consist of any
hydrophilic polymer or combination of polymers with or without
additives as is well known in the art.
If desired, the ink receiving layer can be overcoated with an
ink-permeable, anti-tack protective layer, such as, for example, a
layer comprising a cellulose derivative or a cationically-modified
cellulose derivative or mixtures thereof. An especially preferred
overcoat is poly
.beta.-1,4-anhydro-glucose-g-oxyethylene-g-(2'-hydroxypropyl)-N,N-dimethyl
-N-dodecylammonium chloride. The overcoat layer is non porous, but
is ink permeable and serves to improve the optical density of the
images printed on the element with water-based inks. The overcoat
layer can also protect the ink receiving layer from abrasion,
smudging, and water damage. In general, this overcoat layer may be
present at a dry thickness of about 0.1 to about 5 .mu.m,
preferably about 0.25 to about 3 .mu.m.
In practice, various additives may be employed in the ink receiving
layer and overcoat. These additives include surface active agents
such as surfactant(s) to improve coatability and to adjust the
surface tension of the dried coating, acid or base to control the
pH, antistatic agents, suspending agents, antioxidants, hardening
agents to cross-link the coating, antioxidants, UV stabilizers,
light stabilizers, and the like. In addition, a mordant may be
added in small quantities (2%-10% by weight of the base layer) to
improve waterfastness. Useful mordants are disclosed in U.S. Pat.
No. 5,474,843.
The layers described above, including the ink receiving layer and
the overcoat layer, may be coated by conventional coating means
onto a transparent or opaque support material commonly used in this
art. Coating methods may include, but are not limited to, blade
coating, wound wire rod coating, slot coating, slide hopper
coating, gravure, curtain coating, and the like. Some of these
methods allow for simultaneous coatings of both layers, which is
preferred from a manufacturing economic perspective.
The DRL (dye receiving layer) is coated over the tie layer or TL at
a thickness ranging from 0.1-10 .mu.m, preferably 0.5-5 .mu.m.
There are many known formulations which may be useful as dye
receiving layers. The primary requirement is that the DRL is
compatible with the inks which it will be imaged so as to yield the
desirable color gamut and density. As the ink drops pass through
the DRL, the dyes are retained or mordanted in the DRL, while the
ink solvents pass freely through the DRL and are rapidly absorbed
by the TL. Additionally, the DRL formulation is preferably coated
from water, exhibits adequate adhesion to the TL, and allows for
easy control of the surface gloss.
For example, Misuda et al in U.S. Pat. Nos. 4,879,166; 5,264,275;
5,104,730; 4,879,166, and Japanese Patents 1,095,091; 2,276,671;
2,276,670; 4,267,180; 5,024,335; and 5,016,517 disclose aqueous
based DRL formulations comprising mixtures of psuedo-bohemite and
certain water soluble resins. Light in U.S. Pat. Nos. 4,903,040;
4,930,041; 5,084,338; 5,126,194; 5,126,195; and 5,147,717 disclose
aqueous-based DRL formulations comprising mixtures of vinyl
pyrrolidone polymers and certain water-dispersible and/or
water-soluble polyesters, along with other polymers and addenda.
Butters et al in U.S. Pat. Nos. 4,857,386 and 5,102,717 disclose
ink-absorbent resin layers comprising mixtures of vinyl pyrrolidone
polymers and acrylic or methacrylic polymers. Sato et al in U.S.
Pat. No. 5,194,317 and Higuma et al in U.S. Pat. No. 5,059,983
disclose aqueous-coatable DRL formulations based on poly(vinyl
alcohol). Iqbal in U.S. Pat. No. 5,208,092 discloses water-based
IRL formulations comprising vinyl copolymers which are subsequently
cross-linked. In addition to these examples, there may be other
known or contemplated DRL formulations which are consistent with
the aforementioned primary and secondary requirements of the DRL,
all of which fall under the spirit and scope of the current
invention.
The preferred DRL is 0.1-10 micrometers thick and is coated as an
aqueous dispersion of 5 parts alumoxane and 5 parts poly(vinyl
pyrrolidone). The DRL may also contain varying levels and sizes of
matting agents for the purpose of controlling gloss, friction,
and/or fingerprint resistance, surfactants to enhance surface
uniformity and to adjust the surface tension of the dried coating,
mordanting agents, antioxidants, UV absorbing compounds, light
stabilizers, and the like.
Although the ink-receiving elements as described above can be
successfully used to achieve the objectives of the present
invention, it may be desirable to overcoat the DRL for the purpose
of enhancing the durability of the imaged element. Such overcoats
may be applied to the DRL either before or after the element is
imaged. For example, the DRL can be overcoated with an
ink-permeable layer through which inks freely pass. Layers of this
type are described in U.S. Pat. Nos. 4,686,118; 5,027,131; and
5,102,717. Alternatively, an overcoat may be added after the
element is imaged. Any of the known laminating films and equipment
may be used for this purpose. The inks used in the aforementioned
imaging process are well known, and the ink formulations are often
closely tied to the specific processes, i.e., continuous,
piezoelectric, or thermal. Therefore, depending on the specific ink
process, the inks may contain widely differing amounts and
combinations of solvents, colorants, preservatives, surfactants,
humectants, and the like. Inks preferred for use in combination
with the image recording elements of the present invention are
water-based, such as those currently sold for use in the
Hewlett-Packard Desk Writer 560C printer. However, it is intended
that alternative embodiments of the image-recording elements as
described above, which may be formulated for use with inks which
are specific to a given ink-recording process or to a given
commercial vendor, fall within the scope of the present
invention.
Smooth opaque bases are useful in combination with silver halide
images because the contrast range of the silver halide image is
improved and show through of ambient light during image viewing is
reduced. The photographic element of this invention is directed to
a silver halide photographic element capable of excellent
performance when exposed by either an electronic printing method or
a conventional optical printing method. An electronic printing
method comprises subjecting a radiation sensitive silver halide
emulsion layer of a recording element to actinic radiation of at
least 10.sup.-4 ergs/cm.sup.2 for up to 100 .mu. seconds duration
in a pixel-by-pixel mode wherein the silver halide emulsion layer
is comprised of silver halide grains is also suitable. A
conventional optical printing method comprises subjecting a
radiation sensitive silver halide emulsion layer of a recording
element to actinic radiation of at least 10.sup.-4 ergs/cm.sup.2
for 10.sup.-3 to 300 seconds in an imagewise mode wherein the
silver halide emulsion layer is comprised of silver halide grains
as described above. This invention in a preferred embodiment
utilizes a radiation-sensitive emulsion comprised of silver halide
grains (a) containing greater than 50 mole percent chloride based
on silver, (b) having greater than 50 percent of their surface area
provided by {100} crystal faces, and (c) having a central portion
accounting for from 95 to 99 percent of total silver and containing
two dopants selected to satisfy each of the following class
requirements: (i) a hexacoordination metal complex which satisfies
the formula:
wherein n is zero, -1, -2, -3, or -4; M is a filled frontier
orbital polyvalent metal ion, other than iridium; and L.sub.6
represents bridging ligands which can be independently selected,
provided that at least four of the ligands are anionic ligands, and
at least one of the ligands is a cyano ligand or a ligand more
electronegative than a cyano ligand; and (ii) an iridium
coordination complex containing a thiazole or substituted thiazole
ligand. Preferred photographic imaging layer structures are
described in EP Publication 1 048 977. The photosensitive imaging
layers described therein provide particularly desirable images on
the base of this invention.
The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
EXAMPLES
Example 1
In this example, an image element of the invention having excellent
durability, image structure was created by using a polyolefin
coated paper base, and acrylic pressure sensitive adhesive and a
composite carrier sheet containing a polyester core with rough
surface layer for efficient transport though image printers. This
example will show the utility of the invention materials in
advertising display and the significant reduction in surface
roughness.
Pragmatic sheet;
Paper base was produced using a standard fourdrinier paper machine
and a blend of mostly bleached hardwood Kraft fibers. The fiber
ratio consisted primarily of bleached poplar (25%) and maple/beech
(50%) with lesser amounts of birch (18%) and softwood (7%). Fiber
length was reduced from 0.73 mm length weighted average as measured
by a Kajaani FS-200 to 0.55 mm length using high levels of conical
refining and low levels of disc refining. Fiber Lengths from the
slurry were measured using an FS-200 Fiber Length Analyzer (Kajaani
Automation Inc.). Energy applied to the fibers indicated by the
total Specific Net Refining Power (SNRP) was 1.15 KW hr/metric ton.
Two conical refiners were used in series to provide the total
conical refiners SNRP value. This value was obtained by adding the
SNRPs of each conical refiner. Two disc refiners were similarly
used in series to provide a total Disk SNRP. Neutral sizing
chemical addenda, utilized on a dry weight basis, included alkyl
ketene dimer at 0.20% addition, cationic starch (1.0%),
polyaminoamide epichlorhydrin (0.50%), polyacrylamide resin
(0.18%), diaminostilbene optical brightener (0.20%), and sodium
bicarbonate. Surface sizing using hydroxyethylated starch and
sodium chloride was also employed but is not critical to the
invention. In the 3.sup.rd Dryer section, ratio drying was utilized
to provide a moisture bias from the face side to the wire side of
the sheet. The face side (emulsion side) of the sheet was then
remoisturized with conditioned steam immediately prior calendering.
Sheet temperatures were raised to between 76.degree. C. and
93.degree. C. just prior to and during calendering. The paper was
then calendered to an apparent density of 1.06. Moisture levels
after the calender was 8.4% by weight. The paper base for the
pragmatic sheet has a basis weight of 127 g/m.sup.2 and thickness
of 0.1104 mm.
The paper base was melt extrusion coated on both sides using a
typical extrusion grade polyethylene which had a density of 0.925
g/cc and a melt index of 14.0. The polyethylene contained 18% by
weight of anatase form of TiO.sub.2 with a mean particle size of
0.22 micrometers.
Pressure sensitive adhesive; Permanent solvent based acrylic
adhesive 18 .mu.m thick containing 6% by weight of rutile form of
TiO.sub.2 with a mean particle size of 0.30 micrometers and 0.20%
of tin oxide used for an antistat.
Carrier sheet; The core of the carrier sheet was 140 micrometer
thick biaxially oriented polyester containing primer layers of
polyethylene amine applied to both sides. Adjacent to the
polyethylene amine primer layers was 50 micrometers thick layers of
polyethylene. The outermost surface layer of the carrier sheet had
a roughness average of 0.38 micrometers and was created by casting
the polyethylene against a chilled roller with roughness features
with an roughness average of 0.38 micrometers. Opposite the rough
polyethylene layer was a layer of UV cured silicone for adhesive
release.
Imaging layer; Applied to the outermost surface of the pragmatic
sheet was a typical color light sensitive silver halide imaging
layers as utilized in photographic color printing papers.
The construction of the imaging element of the invention was as
follows;
Light sensitive silver halide imaging layers
Cellulose paper pragmatic sheet
Acrylic pressure sensitive adhesive
Polyester/polyethylene carrier sheet
The resulting imaging element had an overall thickness of 300
micrometers, had a stiffness of 380 millinewtons in the machine
direction and a light transmission of 3.8%. The image element was
printed, processed, the carrier sheet removed and applied to
several different substrates that are commonly utilized in the
advertising display industry. The substrates utilized in the
example were paper board, acrylic sheets, fabric, glass, velvet,
cardboard and wall board. Because the pragmatic sheet of the
invention was thick and durable, the roughness of the substrates
utilized was reduced by an average of 91% allowing rougher, less
expensive materials to be utilized in the display industry. Because
the pragmatic sheet was constructed using polyethylene layers, the
polyethylene provided a conformable layer allowing improvements
over prior art biaxially oriented pragmatic sheets. The rough
polyethylene surface layer of the carrier sheet allowed for
efficient transport through the photographic printer and
processor.
Further, by pressure sensitive laminating the opaque high quality
image member of the invention to the above listed substrates, the
complexities to printing and processing these substrates materials
in a silver halide process are removed. Further, only one opaque
imaging member was required to create several differentiated
product offerings creating savings for the commercial labs and
allowing the commercial lab to utilize silver halide images in a
unique fashion. Additionally, the silver halide image layers of the
invention have also been optimized to accurately replicate flesh
tones, providing superior images of people compared to alternate
flexographic printing technologies.
While this example was directed towards silver halide printing of
images, other high quality imaging techniques such as ink jet
printing, thermal dye transfer printing and electrophotographic
printing can be used in combination with the functional bases of
the invention to create a new image utility. Further, while this
example was directed toward commercial advertising, the invention
materials can be used to improve the image utility for consumers
and professionals alike. Examples include double sided prints, back
illuminated wedding album images, photographic wallpaper and ink
jet printed automobile interiors.
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